1. Field of the Invention
The present invention relates to a noncontact power feeding type power feeding device, power receiving device and wireless power feeding system for supplying and receiving power in a noncontact (wireless) manner.
2. Description of the Related Art
The electromagnetic induction method is known to supply power wirelessly.
On the other hand, recent years have seen attention focused on wireless power feeding and charging systems using a method called the magnetic field resonance method that relies on the electromagnetic resonance phenomenon.
The currently popular noncontact feeding method based on the electromagnetic induction method requires that the source and destination of power (power receiving side) have to share a magnetic flux. For efficient power transmission, the source and destination of power have to be arranged extremely close to each other. Further, coupling alignment is also essential.
On the other hand, the noncontact power feeding method based on the electromagnetic resonance phenomenon is advantageous in that it allows for power transmission over a longer distance than the electromagnetic induction method thanks to the principle of the electromagnetic resonance phenomenon, and that the transmission efficiency does not degrade much even with somewhat poor alignment.
It should be noted that the electric field resonance method is another method based on the electromagnetic resonance phenomenon.
For example, Patent Document 1 discloses a wireless power feeding system relying on the electromagnetic induction method.
The technique disclosed in JP-T-2006-518179 (hereinafter referred to as Patent Document 1) detects the change in load with a circuit sensor in the noncontact power feeding device and changes the inductance of the variable inductor and the capacitance of the variable capacitor, thus ensuring optimal operating frequency of the system.
In other words, the technique disclosed in Patent Document 1 adjusts the circuit if the operating frequency is not optimal.